Hey all! I've got a Jr Pacman (field kit) in, and I wanted a little advice.
PROBLEM:
Jr Pacman constantly resets.
INFO:
z80, RAM, and ROMs have been tested.
Board passes AUTO, BUS, ROM, and Long RAM tests on the Fluke.
I can read ROMs and R/W to RAM manually just fine.
5V ok.
Clocks ok.
So, the way this is supposed to work is 4C watches activity on the address lines, R/W, and Clk, and sends a watchdog pulse every so often to disable the reset at 11C. I have activity on pins 1-6, but no activity on pin 12. I have replaced this LS138 with no improvement, and the old one tested fine.
Schematic (http://www.crazykong.com/manuals/JrPacMan.man.pdf) Page 26 and 37.
At this point, I'd think it should boot but it does not. Screen shows normal boot sequence until it resets. Disabling reset circuit results in a lock after video RAM test.
I suspect PALs at 9C and 8C (pg 30), but I know of no way of testing or replacing them at the moment.
Any ideas?
Thanks in advance
-GB
PROBLEM:
Jr Pacman constantly resets.
INFO:
z80, RAM, and ROMs have been tested.
Board passes AUTO, BUS, ROM, and Long RAM tests on the Fluke.
I can read ROMs and R/W to RAM manually just fine.
5V ok.
Clocks ok.
So, the way this is supposed to work is 4C watches activity on the address lines, R/W, and Clk, and sends a watchdog pulse every so often to disable the reset at 11C. I have activity on pins 1-6, but no activity on pin 12. I have replaced this LS138 with no improvement, and the old one tested fine.
Schematic (http://www.crazykong.com/manuals/JrPacMan.man.pdf) Page 26 and 37.
At this point, I'd think it should boot but it does not. Screen shows normal boot sequence until it resets. Disabling reset circuit results in a lock after video RAM test.
I suspect PALs at 9C and 8C (pg 30), but I know of no way of testing or replacing them at the moment.
Any ideas?
Thanks in advance
-GB
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